Solid ink jet printers generally have print head driver or controller chips that control the voltages sent to the actuators. The actuators convert the voltages received into mechanical energy that pushes ink drops out of apertures (or “jets”) to form images on a print surface. Control of the actuators controls the sizes of the drops and the velocity at which they exit the apertures.
Manufacturing variances can affect both the size and the velocity of ink drops. Typically, print heads undergo testing after manufacture to determine the nature and magnitude of the variances. A process referred to as “normalization” adjusts the voltage applied to each actuator corresponding to each jet to cause the jet to expel ink drops of a standard size and at a standard velocity within some tolerance range. Typically, the normalization process employs at least one transistor as part of the driver chip circuitry, typically on the outputs.
Within the semiconductor layers used to form the transistors “body diodes” generally form. The “body diodes” consists of PN junctions between the source/channel and drain regions of the transistors, typically field-effect transistor (FETs), such as in MOSFETs (metal oxide semiconductor FETs). The body diodes form base and emitter terminals of parasitic, bi-polar junction transistors. The collector terminals of these bi-polar junction transistors may be the chip substrate.
The body diodes conduct current during the trailing edges of high-voltage pulses used in the actuation circuitry. This current causes parasitic current to the chip substrate, creating unwanted power dissipation within the chip. Newer trench-isolated silicon chip processes, while advantageous for print head driver chip fabrication, have even higher gain in these parasitic bi-polar transistors, resulting in higher parasitic current flowing to the chip substrate.